What color of a star depends on?

The colour of a star depends on its temperature.

Massive main sequence stars can have surface temperatures of 50,000 K. Smaller stars such as the Sun have surface temperatures of a few thousand K. Red giants have relatively low surface temperatures of about 3,600 K, but are still very bright.

'K' or 'Kelvin' is a temperature measurement, with 0 Kelvin equal to absolute zero equal to -273oC.